1. Field of the Invention
The present invention relates to a laminated electronic component and a method for manufacturing the laminated electronic component. In particular, the present invention relates to a laminated electronic component including an inner conductor and an outer terminal electrode connected to the inner conductor and formed at least by directly plating an outer surface of an electronic component body, and a method for manufacturing the laminated electronic component.
2. Description of the Related Art
In recent years, the market of compact portable electronic devices such as cellular phones, notebook computers, digital cameras, and digital audio devices has been expanding. These portable electronic devices have been reduced in size and also improved in performance. Such portable electronic devices include a large number of laminated ceramic electronic components. There is a demand for laminated ceramic electronic components that have a reduced size and improved performance. For example, there is a demand for laminated ceramic capacitors that have a smaller size and a higher capacitance.
One technique for effectively obtaining a laminated ceramic capacitor that has a smaller size and a higher capacitance is to reduce the thickness of a ceramic layer. Recently, capacitors having a ceramic layer with a thickness of about 3 μm or less have been produced for commercial use. At present, an even thinner ceramic layer is being pursued. However, since a thinner ceramic layer results in a higher possibility of short circuiting between inner electrodes, it is difficult to produce laminated ceramic capacitors having sufficient quality.
Another technique for effectively producing a laminated ceramic capacitor that has a smaller size and a higher capacitance is to increase the effective area of inner electrodes. However, when laminated ceramic capacitors are produced in volume, side margins between inner electrodes and the side surfaces of a ceramic assembly and end margins between the inner electrodes and the end surfaces of the ceramic assembly are required to compensate for displacement occurring among laminated ceramic green sheets and displacement caused by cutting of the laminated ceramic green sheets. Thus, to increase the effective area of inner electrodes while maintaining the margins, the area of each ceramic layer must be increased. However, an increase in the area of each ceramic layer is restricted by set dimensional specifications of a product. Additionally, the thickness of outer terminal electrodes prevents an increase in the area of each ceramic layer.
Outer terminal electrodes of laminated ceramic capacitors have been formed by applying a conductive paste to the end surfaces of a ceramic assembly and firing the applied conductive paste. Typically, a conductive paste is applied by immersing an end surface of a ceramic assembly into a paste bath and removing the ceramic assembly from the paste bath. Unfortunately, this method tends to produce a thick application of the conductive paste in the central portions of the end surfaces of a ceramic assembly due to the viscosity of the conductive paste. As a result, outer terminal electrodes have thick portions (specifically, the thickness exceeds about 30 μm). Thus, the area of each ceramic layer has to be reduced in accordance with the increase in the thickness of the outer terminal electrodes.
To overcome this problem, a method has been proposed in which outer terminal electrodes are formed by direct plating. In this method, a plating film is deposited using the exposed portions of inner electrodes on an end surface of a ceramic assembly as nuclei. Growth of the plating film results in neighboring exposed portions of inner electrodes being connected to each other. Electrode films formed by this method are thinner and flatter than electrode films formed by existing electrode film formation methods using conductive pastes (see, for example, International Publication No. WO 2007/049456).
However, the formation of outer terminal electrodes by direct plating causes a problem. Specifically, when an outer terminal electrode is formed by directly plating an outer surface of an electronic component body (ceramic assembly) and the resultant plating film defining the outer terminal electrode is includes metal particles having a large average size, such as 1 μm or more, the number of gaps formed at grain boundaries, which channels for moisture to escape, is decreased. When the electronic component body is heat treated to remove moisture, hydrogen molecules, and hydrogen ion from the inside of the electronic component body, these substances tend to remain inside the electronic component body. Use of such an electronic component body results in decreased reliability. For example, the properties, such as insulation resistance, degrade with the passage of usage time.